PubMed Health⌕ Search

Biomedical subjects

B Sears

Publications and source records attributed to B Sears.

At least 19 recordsLinked to original sources
PubMed2000

Complete nucleotide sequence of the Oenothera elata plastid chromosome, representing plastome I of the five distinguishable euoenothera plastomes.

We describe the 159,443-bp [corrected] sequence of the plastid chromosome of Oenothera elata (evening primrose). The Oe. elata plastid chromosome represents type I of the five genetically distinguishable basic plastomes found in the subsection Euoenothera. The genus Oenothera provides an ideal system in which to address fundamental questions regarding the functional integration of the compartmentalised genetic system characteristic of the eukaryotic cell. Its highly developed taxonomy and genetics, together with a favourable combination of features in its genetic structure (interspecific fertility, stable heterozygous progeny, biparental transmission of organelles, and the phenomenon of complex heterozygosity), allow facile exchanges of nuclei, plastids and mitochondria, as well as individual chromosome pairs, between species. The resulting hybrids or cybrids are usually viable and fertile, but can display various forms of developmental disturbance.

Base Sequence↗
PubMed1985

Deuterium NMR spectroscopy of biosynthetically deuterated mammalian tissues.

The choline-containing phospholipids of mammalian membranes have been biosynthetically deuterated by raising rats on a diet supplemented with [HOCH2CH2N(CD3)3]+Cl- or [HOCD2CH2N(CH3)3]+Cl-. Deuterium NMR spectra have been obtained from excised deuterated brain, sciatic nerve, heart, and lung, from isolated brain myelin and brain microsomes, and from aqueous dispersions of lipid extracts. Measurements of residual quadrupole splittings for excised deuterated neural tissues demonstrate that the orientational order of the choline head group is similar to that observed in model membranes. The spin-lattice relaxation time of the choline head group in deuterated neural tissue is indistinguishable from that observed in model membranes. These results support the proposal that the conformation and motional dynamics of the choline head groups of the bulk choline-containing lipids of neural tissue are similar to those in model membranes. Spectra of biosynthetically deuterated brain myelin and brain microsomes exhibit similar quadrupole splittings. Since these membranes have significantly different protein contents, these results indicate that no strong polar interactions exist between membrane proteins and the choline head groups of choline-containing membrane lipids. Spectra of intact deuterated heart and lung exhibit broad lines and a range of quadrupole splittings. Due to the heterogeneous nature of these tissues, interpretation is difficult. However, no strong ordering of the lipid head group by protein is indicated.

Animals↗
PubMed1985

A calorimetry and deuterium NMR study of mixed model membranes of 1-palmitoyl-2-oleylphosphatidylcholine and saturated phosphatidylcholines.

Binary phase diagrams have been constructed from differential scanning calorimetry (DSC) data for the systems 1-palmitoyl-2-oleylphosphatidylcholine (POPC)/dimyristoylphosphatidylcholine (DMPC), POPC/dipalmitoylphosphatidylcholine (DPPC) and POPC/distearoylphosphatidylcholine (DSPC). Mixtures of POPC with DMPC exhibit complete miscibility in the gel and liquid crystalline states. Mixtures of POPC with DPPC or with DSPC exhibit gel phase immiscibility over the composition range 0-75% DPPC (or DSPC). These results, when taken together with previous studies of mixtures of phosphatidylcholines, are consistent with the hypothesis that PCs whose order-disorder transition temperatures (Tm values) differ by less than 33 deg. C exhibit gel state miscibility. Those whose Tm values differ by more than 33 deg. C exhibit gel state immiscibility. 2H-NMR spectroscopy has been used to further study mixed model membranes composed of POPC and DPPC, in which either lipid has been labeled with deuterium in the 2-, 10- or 16-position of the palmitoyl chain(s) or in the N-methyls of the choline head group. POPC/DPPC mixtures in the liquid crystalline state are intermediate in order between pure POPC and DPPC at the same temperature. The POPC palmitoyl chain is always more disordered than the palmitoyl chains of DPPC in liquid crystalline POPC/DPPC mixtures. This is attributed to the fact that a POPC palmitoyl chain is constrained by direct bonding to have at least one oleyl chain among its nearest neighbors, while a DPPC palmitoyl chain must have at least one neighboring palmitoyl chain. When liquid crystalline POPC, DPPC and POPC/DPPC mixtures are compared at a reduced temperature (relative to the acyl chain order-disorder transition), POPC/DPPC mixtures are more disordered than predicted from the behavior of the pure components, in agreement with enthalpy data derived from DSC studies. Within the temperature range of the broad phase transition of 1:1 POPC/DPPC, a superposition of gel and liquid crystalline spectra is observed for 1:1 POPC/[2H]DPPC, while 1:1[2H]POPC/DPPC exhibits only a liquid crystalline spectrum. Thus, at temperatures within the phase transition region, the liquid crystalline phase is POPC-rich and the gel phase is DPPC-rich. Comparison of the liquid crystalline quadrupole splittings within the thermal phase transition range suggests that mixing of the residual liquid crystalline POPC and DPPC is highly non-ideal.

Calorimetry, Differential Scanning↗
PubMed1983

Deuterium nuclear magnetic resonance studies of bile salt/phosphatidylcholine mixed micelles.

Mixed micelles of deoxycholate (DOC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) have been prepared in which the POPC was specifically deuterated in the 2-, 6-, 10-, or 16-position of the palmitoyl chain or in the N-methyl position of the choline head group. The deuterium nuclear magnetic resonance (2H NMR) spectrum of each of these specifically deuterated mixed micelles consists of a singlet whose line width depends upon the position of deuteration. Spin-spin relaxation times indicate a gradient of mobility along the POPC palmitoyl chain in the mixed micelle, with a large increase in mobility on going from the 10- to the 16-position. Spin-lattice relaxation times (T1's) demonstrate a similar gradient of mobility. Both trends in NMR relaxation behavior are consistent with a bilayer arrangement for the solubilized POPC. 2H T1 times for DOC/POPC micelles are significantly shorter than those measured in other bilayer systems, indicating unusually tight phospholipid acyl chain packing in the mixed micelle.

Deoxycholic Acid↗
PubMed1982

Order and fluidity in the terminal methyl region of dipalmitoyl phosphatidylcholine multibilayers: a comparison of Raman and 2H-NMR spectroscopy.

Deuterium magnetic resonance (2H-NMR) and Raman spectroscopy are used to investigate order and fluidity at the terminal methyl position in 16-d3, 16'-d3 dipalmitoylphosphatidyl-choline (16-d6 DPPC) multibilayers. These methods reveal substantial motion and disorder in the gel phase, 5-10 degree C below the gel-liquid crystal phase transition temperature (Tm). The phase transition is sensed in the 2H-NMR spectrum as a reduction in the quadrupole splitting from 14 kHz to approximately 3 kHz. In contrast, the Raman parameter used to characterize the CD3 vibrations is quite insensitive to the melting process, although an analagous parameter does sense disordering at Tm at the 10 and 10' position in 10-d2, 10'-d2 DPPC. The difference in the response of the NMR and Raman parameters may arise because the vibrational spectrum of the CD3 group is inhomogeneously broadened and is therefore quite sensitive to alterations in the local environment around the methyl group. In contrast, the NMR quadrupole splitting is sensitive to both local motion of the methyl group and, near Tm, to motions of the CD2 group induced by transgauche isomerizations further up the chain. The difficulties that arise when results from different spectroscopic techniques are compared are demonstrated.

Lipid Bilayers↗
PubMed1979

Deuterium NMR studies of cerebroside-phospholipid bilayers.

2H-NMR was used to probe the interaction of non-hydroxy fatty acid cerebroside and 2-hydroxy fatty acid cerebroside with the polar head group and with the acyl chains of dipalmitoylphosphatidylcholine in unsonicated bilayers. It is shown that the interior of the bilayer exhibits uniformly increasing orientational order as the concentration of both types of cerebroside increases, whereas the surface of the bilayer, as reflected by the head group motion, becomes disordered. The extent of the disorder at the surface is dependent upon the type and concentration of the cerebroside. These results are discussed in terms of hydrogen-bonding interactions.

Cerebrosides↗
PubMed1976

Temperature-dependent 13C nuclear magnetic resonance studies of human serum low density lipoproteins.

The natural abundance 13C nuclear magnetic resonance (NMR) spectrum of human serum low density lipoproteins (LDL) shows significant temperature-dependent changes. These temperature-dependent spectra have been used to monitor changes in the organization of cholesterol esters within the LDL particle. Comparison with 13C NMR spectra of both cholesterol linoleate and an aqueous codispersion of cholesterol linoleate and egg phosphatidylcholine suggests that at low temperatures (10 degrees C), the cholesterol esters in LDL are organized in a smectic-like, liquid-crystalline arrangement. At temperatures above the order-disorder transition exhibited by the cholesterol esters of LDL, the cholesterol esters appear to be partially melted but still are motionally restricted compared with liquid cholesterol esters.

Carbon Isotopes↗
PubMed1976

Effects of paramagnetic shift reagents on the 13C nuclear magnetic resonance spectra of egg phosphatidylcholine enriched with 13C in the N-methyl carbons.

Effects of paramagnetic shift reagents on the 13C NMR spectra obtained from single-walled vesicle dispersions of egg phosphatidylcholine enriched with 13C in the N-methyl carbons are investigated. Spectra obtained at 25.1 MHz show that, at Yb3+ to phospholipid molar ratios as low as 0.06, complete resolution of the N-methyl carbon resonances is obtained from molecules on the inner and outer faces of the vesicle bilayer. No precipitation of the vesicles is caused by Yb3+ at these concentrations nor is appreciable line broadening observed. Other paramagnetic shift reagents frequently used in proton NMR investigations of phosphatidylcholine vesicles do not give complete separation of the N-methyl 13C signals from the two bilayer surfaces. K3Fe(CN)b,Eu3+, and Pr3+ cause precipitation of the phosphatidylcholine vesicles at concentrations, which give only incomplete resolution of these signals. T1 measurements of the resonances separated by Yb3+ indicate that the choline groups on the inner bilayer surface are less mobile than are the same groups in the outer surface. Gated proton decoupling measurements, which show that the nuclear Overhauser effect is 2.8 +/- 0.1, indicate that the dominant mode of relaxation is dipolar interaction.

Carbon Isotopes↗
PubMed1975

13C nuclear magnetic resonance studies of egg phosphatidylcholine.

Spin lattice relaxation times (T1) and apparent spin-spin relaxation times (T2) derived from linewidth have been used to investigate model membranes composed of egg yolk phosphatidylcholine. T1 measurements appear to be largely dominated by segmental motion and as a consequence are not very sensitive to small changes in membrane structure. On the contrary, apparent T2 times are shown to be sensitive to such changes in the membrane and are thus suggested as a useful tool for further investigation of membrane structure.

Carbon Isotopes↗